PPRuNe Forums - View Single Post - Air India B788 descends to 200 ft over water at HKG
Old 21st Dec 2018, 19:06
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pattern_is_full
 
Join Date: Jan 2008
Location: Denver
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Due to the TWY - GS antenna configuration the same was an issue at SVO for 25L (it's been a while).
Yes - the geometry of a GS antenna is fixed everywhere - the antenna is, by definition, the place where the G/S beam intersects the ground. ~300m/1000 feet beyond the threshold "piano keys." Thus a taxiway that meets the threshold at 90° (extremely common) will also always be ~300m from the G/S antenna, and risk a holding/taxiing aircraft becoming an obstruction.

Workarounds can only be done by adjusting the taxiways to not lead directly to the threshold at 90°, or changing ops otherwise: displaced threshold; long looping taxiway that connects to the threshold at 0°, all departures from an intersection beyond the G/S antenna; back-taxiing from an intersection for >300m (probably not a good idea when another aircraft is inbound inside the marker - and might still produce interference). Switching to a 6° GS would put the beam angle "above" even tall aircraft that might block the signal - maybe.

All of which produce their own issues.
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